1. Field of the Invention
The present invention relates generally to an inflatable packer attached to a supporting element for sealing an annular space in a well bore and, more particularly, to an improved inflatable packer having a high pressure resistance. Specifically, the present invention relates to inflatable packers having improved reinforcement structure to prevent premature failure under high pressure conditions.
2. Description of the Prior Art
Inflatable packers are down-hole tools useful in the well drilling industry as well as in other piping applications. An inflatable packer is internally inflatable utilizing a fluid for the purpose of sealing off an annular space in the well or pipe, for example, between the casing and the well bore, or between a drill string or other retrievable tool in an outer well casing. Although not so limited, the packer of the present invention is particularly suited for isolating zones within a well for such purposes as cementing, fracturing, treating, testing, preventing gas migration to the surface and for gravel pack operations.
Inflatable packers normally include an elastomeric body and a reinforcement sheath or layer. The elastomeric tubular body is adapted for inflation such that the center portion extends radially outwardly to forcibly engage the well bore or well casing thereby positioning the packer and the well. Typically, the inflatable portion of the packer includes a center portion which is uniformly inflated so as to provide a collar or sleeved area engaged with the well bore. The ends of the packer have couplings to enable the packer to be attached to a drill string, and the area between the couplings and the center portion is a transition zone that is gradually expanded from the narrow non-expanded coupling to the fully expanded center portion.
Typically, the reinforcement elements or sheaths may include a plurality of strain-resistant elements or cords of high modulus that extend helically about the tubular body in one or more layers or plies. These reinforcement elements are then clamped or in some other manner attached at their ends to the end couplings of the packers so as to terminate at the end couplings. An example of one such arrangement is illustrated in U.S. Pat. No. 4,614,346. The angle that the reinforcement elements make relative to the longitudinal axis of the tubular elastomeric body is known as the lay angle inasmuch as this is the angle at which the helically wound elements are laid up around the uninflated tubular body. When the packer is inflated, the angle that the cords make relative to the longitudinal axis is known as the angle of equilibrium between the hoop tension and the axial tension of the cord, since it is at an angle to the longitudinal axis. A specific, specialized equilibrium angle is known in the hose art as the lock angle, i.e., 54.degree. 40', at which point the cords provide maximum reinforcement strength relative to radial expansion of the rubber hose.
Recognized problems with prior packers have been the inability to securely anchor reinforcing elements of the packer body to end sleeve or coupling members during inflation due to the axial force created on the reinforcement members as the tube expands radially outwardly and the reinforcing members are stretched away from the coupling connections. In addition, there is a tendency for the reinforcing elements to separate from each other and permit elastomeric material to be pressured up between them, thereby providing weak spots in the reinforcement subject to pinhole leaks and eventual blow-outs at the expansion area of the packer. Again, U.S. Pat. No. 4,614,346 attempts to alleviate this problem by providing multiple layers of helical wound reinforcing elements, with each layer having alternate lay angle winds with respect to the packer axis. Examples of other prior art devices which attempt to alleviate the aforementioned problems include those disclosed in U.S. Pat. No. 2,643,722, No. 2,872,230, No. 2,970,651, No. 3,028,915, No. 3,035,639, No. 4,191,383, No. 4,700,954, and Canadian Patent No. 702,327.
Another attempt at enhancing the performance of such inflatable packers and reduce the premature failure rate is included in a related application filed by the inventors of this application simultaneously herewith, that is application Ser. No. 07/784,336 filed on Oct. 29, 1991. In this particular application, enhanced resistance to pressure and enhanced mounting ability of the reinforcement elements at the coupling members was achieved by varying the lay angle from the coupling members toward the center, expansion portion of the packer. Despite this and other numerous attempts, however, to alleviate or at least reduce the aforementioned problems, there is still a need for additional inflatable packer construction designs which further reduce the problems of reinforcement element rupture at their juncture with the end couplings, of the tendency of the elastomeric body of the packer to rupture or develop pinhole leaks, and of the failure of the packer body to return substantially to its original uninflated configuration after repeated inflation/deflation cycles.